I have been meaning to blog about this for some time (no pun intended!)
Simon and Natalie have uploaded the 500 or so files that are in the pytz library so you don't have to and built a JSON API that you can call from your Google App Engine apps.
To get the current time in London, for example, you would call the following URL:
http://json-time.appspot.com/time.json?tz=Europe/London
Check out jsontime.
The jsontime for Google App Engine article by Aral Balkan, unless otherwise expressly stated, is licensed under a Creative Commons Attribution-Noncommercial 2.0 UK: England License.
Really handy!
Awesome, they even have a crossdomain.xml file. If they add year,month,day,dayOfWeek,isDST and UTCOffset it would be complete.